Obesity in humans has steadily increased worldwide. This trend is not just confined to adults-currently, over one-third of U.S. adults are obese-but also evident in children and adolescents. Comorbidities associated with obesity include type 2 diabetes, cancer (e.g., pancreatic and prostate cancers), cardiovascular disease, asthma, gallbladder disease, osteoarthritis, and chronic back pain. The most prevalent comorbidity associated with obesity is type 2 diabetes, which is estimated to cost the United States in excess of $300 billion per year.
Diet plans for preventing or reducing obesity provide often conflicting and sometimes even diametrically opposed advice for which macronutrients promote weight loss. More recently, the “calorie-in/calorie-out” (CICO) model of metabolism has increased in popularity. The use of the calorie to attribute energy to food sources has been in place since the mid-1800s. FIG. 1 is a diagram illustrating the “calorie-in/calorie-out” (CICO) model 100, which posits that an imbalance between a subject's energy needs (calories out 102, e.g., 1500-3000 Cal/day) and the amount of calories that the subject consumes (calories in 104, e.g., 1000-3000 Cal/day) results in either weight gain (virtually unlimited calorie storage 106) or weight loss (calorie burning 108). That is, if the subject consumes calories in excess of the subject's energy needs, the excess calories will not be burned or excreted, but rather stored as glycogen or as adipose tissue, thereby contributing to obesity and comorbidities.
Many diet plans now rely on tracking food calories as a simplistic means to manage weight. Diet plans that are structured around the CICO model promote overt control of calorie intake and/or an exercise regimen to create an energy imbalance.
While the CICO model relies on the first law of thermodynamics (i.e., energy cannot be created or destroyed), the underlying assumption of the CICO model is that all food calories are alike. As such, calorie counting and other diet plans that are structured around the CICO model are not only tedious to implement and prone to error, but often ignore the impact that different macronutrient mixes and exercise intensities have on an individual's homeostatic control system. As a consequence, diet plans focused solely on energy balance (the CICO model) have failed to reduce the worldwide trend of increasing obesity and comorbidities despite their popularity.